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Choice of source photon production in entanglement experiments

  1. Apr 19, 2009 #1
    Just a quick question regarding the sources used for investigating entanglement (of photons). There are two types of production method as I understand it:

    ('Fundamentals of quantum optics and quantum information', Peter Lambropoulos, David Petrosyan, 2006, Springer): Page 242

    "In fact, most of the experimental tests of Bell's inequalities have been performed using polarization-entangled photon pairs. These include a series of pioneering experiments by Aspect and coworkers, using atomic radiative cascade, as well as a number of experiments by several teams using nonlinear crystals to realize spontaneous parametric down-conversion. In the former experiments, a high-efficiency source of pairs of photons ... was obtained... The polarization entanglement of the photons comes about because of angular momentum conservation. Since relative to photons, the atoms are massive objects, their recoil during photon emission is negligible. Therefore... the propogation directions of the two photons are also strongly correlated, due to energy and momentum conservation. In the experiments with nonlinear crystals... here again, angular momentum is conservation imposes polarization entanglement between the photons, while phase-matching conditions result in a finite angle between propogation directions of the photons, which make it possible to redirect each photon to its own measuring apparatus"

    So my questions is:
    is there anything (other than ease-of-use for the particular experiments conducted) that
    prevents us from swapping source? I.e. could Aspect have used SPDC and the Quantum
    Erasor teams used a radiative cascade source and achieved the same results as they

    This is probably sounds like a really dumb question but I just feel like I'm missing something fundamental here but I can't see what?
  2. jcsd
  3. Apr 19, 2009 #2


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    If PDC had been easily available when Aspect did his work, he probably would have used that. But conceptually, there is no difference. In either case, there are conservation rules that govern the entangled state.
  4. Apr 20, 2009 #3
    Thanks as ever Dr. C.
    I'm thinking about the half-wave plate (e.g. 'Observation of a "quantum eraser": a revival of coherence in a two-photon interference experiment': Kwait, Steinberg, Chiao, Physical Review A, Vol 35, No 11) and I need to think more in order to be able to phrase clearly what I need to ask. I'll have to sleep on it.
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